The present invention relates to apparatus for effecting, by the application of heat and pressure the polymerisation of an adhesive substance interposed between respective facing superimposed portions of respective superimposed connected mechanical elements, typically the internal and external panels of parts of motor body doors made of thermo setting plastics material. The invention further relates to a method for polymerisation of adhesive substances for the purpose of mutually fixing two superimposed connected elements, which can be performed with the said apparatus. It is known that parts of motor vehicle doors made of plastics material, for example the tail gate or doors of motor vehicles, are obtained by superimposing and fixing together two (or more) shaped elements obtained by moulding and constituting the internal panel and the external panel of the door element; this fixing, in particular in the case of composite panels made of thermosetting resin and/or other resins, is effected by gluing them together, there being a continuous bead (or spots) of an adhesive substance spread along the junction edges between the panels, then superimposing these, and finally effecting polymerisation (with consequent achievement of the connection) of the adhesive substance. This polymerisation is generally obtained by the simultaneous action of heat and pressure; the heat serves to accelerate the process of cross-linking the adhesive; the pressure serves to maintain the glued edges adherent to one another until the adhesive has taken grip.
The pressure and the heat necessary for polymerisation are currently provided by clamping the elements to be fixed, already coupled and with the adhesive interposed between them, between two moulds usually made of plastics material and one of which is provided with a weight or with a pressure clamping device and, then, causing the "sandwich" thus formed to pass through a tunnel furnace in which the elements are heated in their entirety to the polymerisation temperature of the adhesive (150.degree.-180.degree. C.) by means of a flow of hot air. This method of proceeding is, however, not free from disadvantages; in the first place the tunnel furnace has large dimensions (more than 20 meters) and a high cost; moreover there is a very high energy consumption due to the considerable heat losses and, above all, to the necessity of having to heat both the elements to be glued as well as the adhesive; finally, the time necessary for the operation is relatively long (nine minutes and more) and this is aggravated by the fact that, after polymerisation, it is necessary to wait for the glued elements to cool (with consequent considerable increase in the cycle time) both to allow manual handling and, above all, to allow the application of electroconductive paints or "primers" necessary to effect the electrostatic painting process subsequent to gluing.